Co‐inoculation of Azospirillum brasilense and late nitrogen fertilization for no‐till soybean production

Abstract

Soybean [Glycine max (L.) Merr.] is highly efficient in the biological N2 fixation (BNF) process through the association of bacteria of the genus Bradyrhizobium in the root nodules of the plants. However, there are still doubts about the need to complement soybean N demand through N fertilization in high‐yield environments. In addition, the real impact of co‐inoculation of soybean with Azospirillum brasilense and Bradyrhizobium spp. is not yet clear in such environments. A field experiment was conducted from 2012 to 2021 with six soybean cropping seasons in a crop rotation scheme with black oat (Avena strigosa Schreb), maize (Zea mays L.), and wheat (Triticum aestivum L.) under no‐till (NT) in Southern Brazil. Soybean seeds were co‐inoculated with A. brasilense (strains Ab‐V5 and Ab‐V6) shortly after inoculation with Bradyrhizobium japonicum, and different levels of N fertilization were used in top dressing at the start of pod formation (R3). Soybean nutritional status and grain yield were not benefited by co‐inoculation with A. brasilense. Since the increased inoculum rate of A. brasilense co‐inoculated with rhizobia in soybean compromised both N nutrition and grain yield, this practice should not be encouraged. There was no need to complement soybean N demand through N fertilization during the reproductive stage. Soybean achieved grain yields of 5.0–5.7 Mg ha−1 and, even so, there was no need to complement N demand through N fertilization. The results suggest that soybean N demand in a high‐yielding environment under NT could be satisfied exclusively through the optimization of BNF.